This application claims the priority of Korean Patent Application No. 2006-11756, filed on Feb. 7, 2006, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a mobile communication terminal and, more particularly, to a mobile communication terminal supporting a teletypewriter (TTY) device for hard-of-hearing or speech-disabled persons.
2. Description of Related Art
A mobile communication terminal provides TTY services to hard-of-hearing or speech-disabled persons. The TTY service receives Baudot tones corresponding to voice or characters from a TTY device, packetizes and transmits the received Baudot tones to a wireless network. Since the mobile communication terminal is connected to the TTY device and supports a vocoder (voice coder) corresponding to the TTY device, a TTY mode needs to be set in the mobile communication terminal.
In more detail, the TTY device is an industrial standard device that transfers a Baudot tone of 45.45 bps and is connected to the mobile communication terminal through a 2.5 mm audio connector (e.g., headset jack or ear jack). Since the TTY device uses the same audio connecter as an earphone, the mobile communication terminal cannot identify whether or not a device connected to the audio connecter is a TTY device. Thus, a user selects a desired TTY mode and notifies the mobile communication terminal of the selected TTY mode.
There are three TTY modes: 1) a Full mode in which a Baudot tone is sent and received for hard-of-hearing or speech-disabled users; 2) a VCO (voice carryover) mode in which voice is sent and a Baudot tone is received for hard-of-hearing but speaking users; and 3) an HCO (hearing carryover) mode in which a Baudot tone is sent and voice is received for speech-disabled but hearing users. The TTY modes, such as Full-to-Full, VCO-to-HCO, or HCO-to-VCO, of mobile communication terminals need to be preset on both transmitter and receiver sides. That is, both of the terminals need to be connected to the TTY devices and TTY modes need to be preset in the terminals.
However, as described above, since the mobile communication terminal cannot identify whether or not a device connected to the audio connecter is a TTY device, a mobile communication terminal on the receiver side cannot determine whether a received voice data packet is voice or Baudot tone. That is, if both of the transmitter and receiver sides do not notify each other beforehand which TTY mode has been preset in the terminals, the receiver side cannot identify whether or not a TTY mode on the transmitter side is in an enable state, or which TTY mode is in an enable state. As a result, there is a problem in that when the transmitter side unilaterally attempts to make a call, the receiver side may conclude the transmitter's terminal or base station to be defective due to an incorrect TTY mode.